1. Field of the Invention
This invention relates to a linear light-emitting diode (LED) lamp, and more particularly to a linear LED lamp with a readily retrofittable modular structure that enables consumers or manufacturers to readily retrofit, maintain, or upgrade the lamp by replacing an LED module or an internal LED driver. With such a retrofittable modular structure, all the workable parts with specifications that meet market demands can be reused to save resources and to reduce waste on the earth.
2. Description of the Related Art
Solid-state lighting from semiconductor light-emitting diodes (LEDs) has received much attention in general lighting applications today. Because of its potential for more energy savings, better environmental protection (no hazardous materials used), higher efficiency, smaller size, and much longer lifetime than conventional incandescent bulbs and fluorescent tubes, the LED-based solid-state lighting will be a mainstream for general lighting in the near future. Meanwhile, as LED technologies develop with the drive for energy efficiency and clean technologies worldwide, more families and organizations will adopt such a “green” LED lighting for their illumination applications. In this trend, even though no hazardous materials are used in an LED lamp, the lamp material reuse becomes an important environmental issue and needs to be well addressed.
Whereas environmental interest groups persist to urge businesses to pay more attention to their environmental policy, Environmental Protection Agency (EPA) continues to encourage people and businesses to conserve energy, reduce waste, and even lower carbon footprint by recycling and reusing materials. On the LED lamp market, quite a number of so called “green” consumers express preferences for products and firms that are recognized to be more environment-friendly than other competitive products and companies. Such green consumers always check potential LED lamps to see if they are either recyclable or made from interchangeable parts. Besides, some green consumers express their concerns about LED lamps' durability, not just to get one at a cheaper price because they know LED lamps that are more durable and repairable will last longer and therefore produce less garbage in the long run. “Green” investors including individuals and organizations always want to put their money where their environmental values are, especially for solid-state lighting—“green” products based on “green” technologies. In this sense, the linear LED tube lamp manufacturers should make an environmental decision to make their products to be more eco-friendly to be successful.
Although LEDs themselves can operate at least 50,000 hours, the LED driver that operates the LEDs in a linear LED tube (LLT) lamp in most cases cannot last so long because of potential failures of a LED driver in which electrolytic capacitors or other electronic components used are likely to fail prematurely. Upon failure, the LED driver needs to be replaced. But if the LED driver, typically about 10-15% of the cost of an LLT lamp, is not cost-effectively replaceable, then the whole lamp needs to be replaced and becomes waste. However, if the LLT lamp is so designed that internal LED driver can be easily removed and replaced, consumers or manufacturers can replace the LED driver only and not the whole lamp. That way, the manufacturers can reuse all other workable parts with specifications that meet market demands and rebuild the LLT lamp, saving about 85-90% of cost of the lamp with all the workable parts including the LED module, lamp bases, heat sink and housing, lens, and so on.
Furthermore, as LED technologies and standards continue to develop rapidly, requirements of an LED luminous efficacy of 100 lumens per watt and a color rendering index (CRI) of 80 today will be unsatisfactory tomorrow to consumers and the Energy Star program. Market also requires a minimum number of surface mount LEDs used in the LED module and a specific correlated color temperature (CCT) tolerance for LED chips. So, for example, a minimum requirement of 264 LEDs in a 4-ft-T8 LLT lamp and a CCT tolerance of 175 K (Kelvin) today may be obsolete tomorrow. Similarly for LED drivers, requirements of a power factor of 0.9, a total harmonic distortion (THD) less than 20%, and a power consumption of 20 W today may not be good enough tomorrow for energy firms to offer energy rebates, a great incentive for consumers and organizations to adopt LED lamps. In this case, outdated LED modules and LED drivers may need to be replaced with upgraded ones to meet updated consumer needs and new standards.
It is, therefore, the manufacturers' environmental responsibility to design a readily retrofittable LLT lamp such that the redesign efforts are beneficial to lifetime cost of ownership and environmental protection. It seems simple and straightforward, but not single one of manufacturers adopts the idea and builds such products today, whereas an LLT lamp costs only several tens of dollars, and price competition continues to be severe on the market; manufacturers are just trying to produce such LLT lamps at the lowest cost.
To retrofit a conventional LLT lamp for replacing an existing LED driver, one must first remove the two end caps and then cut the AC wires that connect to the AC mains through two opposite bi-pins in the two end caps or de-solder the wires from their respective soldering joints in the two end caps. Then one must disconnect DC wires connected between the LED driver and the LED module by cutting or de-soldering the wires from their respective soldering joints/contacts on the LED PCB (printed circuit board). If the LED driver is not mechanically fixed, then it can be removed immediately after all the wires are released. However, the LED driver should be mechanically secured in an LLT lamp, not relying solely on the electrical contacts, to prevent possible electric shock hazards that occur when any one of the wires is accidentally detached from the soldering joint with the exposed conductor touching the metallic housing. Therefore, Underwriters Laboratories (UL) requires the LLT lamp to meet this consumer safety need. If the LED driver is fixed inside an LLT lamp using a rivet, then one needs to first remove the LED PCB on the upper platform of the lamp housing and then drill the rivet out of the place and then remove the LED driver. The replacement work is tedious and labor intensive; when LED PCB is removed from the platform of the aluminum housing, the LED PCB becomes bent, preventing it from reuse. Thus, no manufacturers would like to replace the LED driver even though the LED driver is broken, but would rather replace the whole lamp, leaving the whole non-operable lamp as a piece of garbage. This kind of products is not eco-friendly and will eventually be rejected by consumers, especially by “green” consumers.
Referring to FIGS. 1 and 2, a conventional LLT lamp 100 comprises a housing 110 with a length much greater than its diameter of 25 to 32 mm, two end caps 120 and 130 with bi-pins 180 and 190 respectively on two opposite ends of the housing 110, LED arrays 140 mounted on a printed circuit board (PCB) 150, and an LED driver 160 used to receive energy from the AC mains, 110 V, 220 V, or 277 VAC, through electrical contacts 142 and the bi-pins 180 and 190, to generate a proper DC voltage with a proper current, and to supply it to the LED arrays 140 such that the LEDs 170 on the PCB 150 can emit light. In some conventional LLT lamps, the LED driver wrapped by an insulation paper or a heat shrinking tube is inserted into the LLT lamp without being mechanically secured. The electrical wires connected to the AC mains may come off from the soldering joints at the electrical contacts 142, which may create a safety issue not acceptable for UL and consumers. Therefore, in some conventional LLT lamps, a rivet (not shown) on the upper platform of the housing is used to secure the LED driver in place under the platform. When the LED PCB is attached on the upper platform of the housing, the rivet can no longer be accessed without first detaching LED PCB from the housing. This means that the LED driver cannot be removed unless the rivet is removed first. Soldering joints 152 and 153 are used to connect the LED driver output DC+ and DC− to the LED arrays. The bi-pins 180 and 190 on the two opposite end caps 120 and 130 connect electrically to the AC mains through two electrical sockets located lengthways in an existing fluorescent tube fixture whereas the two sockets in the fixture connect electrically to the line and the neutral wire of the AC mains, respectively. This is a so called “double-ended” configuration.
To replace a fluorescent tube with an LLT lamp 100, one inserts the bi-pin 180 at one end of the LLT lamp 100 into one of the two electrical sockets in the fixture and then inserts the other bi-pin 190 at the other end of the LLT lamp 100 into the other electrical socket in the fixture. When the line power of the AC mains applies to the bi-pin 180 through one socket, and the other bi-pin 190 at the other end is not yet in the other socket in the fixture, the LLT lamp 100 and the LED driver 160 are deactivated because no current flows through the LED driver 160 to the neutral. However, the internal electronic circuitry is live. At this time, if the person who replaces the LLT lamp 100 touches the exposed bi-pin 190, which is energized, he or she will get an electric shock because the current flows to earth through his or her body—a shock hazard.
Almost all the LLT lamps currently available on the market are without any protections for such electric shock. The probability of getting shock is 50%, depending on whether the person who replaces the lamp inserts the bi-pin first to the line of the AC mains or not. If he or she inserts the bi-pin 180 or 190 first to the neutral of the AC mains, then the LLT lamp 100 is deactivated because the internal circuitry is not live—no shock hazard. An LLT lamp supplier may want to adopt single protection only at one end of an LLT lamp in an attempt to reduce the risk of shock during re-lamping. However, such a single protection approach cannot completely eliminate the possibility of shock risk.
An easy solution to reducing the risk of shock is to connect electrically only one of two bi-pins at the two ends of an LLT lamp to the AC mains, leaving the other bi-pin at the other end of the LLT lamp electrically insulated. Thus, the line and the neutral of the AC mains go into the LLT lamp through the single-ended bi-pin, one for “line” (denoted as L, hereafter) and the other for “neutral” (denoted as N, hereafter). The electrically insulated bi-pin at the other end only serves as a lamp holder to support the LLT lamp mechanically in the fixture. The LLT lamp configured this way is therefore called “single-ended”.
In FIG. 3, the AC mains supply voltage to the bi-pin socket 255 in the lamp holder 311 from an end of the LLT lamp 101 leaving the lamp holder 312 electrically insulated—a single ended configuration. Two pins 181 and 182 of the bi-pin are at one end, from which the driver 400 receives energy to power the LED arrays 214. The conductors in the bi-pin socket 255 of the lamp holder 311 are used to connect the bi-pins to the AC mains through electrical contacts shown as dots. The “dot” notation will be used to indicate electrical contacts throughout the figures.
In FIG. 4, the driver 400 receives energy from both bi-pin sockets 255 and 256 in the lamp holders 313 and 314 at opposite ends of the LLT lamp 102 to power the LED arrays 214—a double-ended configuration. The two pins 181 and 182 at one end are internally interconnected with a conductor 253. Similarly, the two pins 183 and 184 at the other end are internally interconnected with a conductor 254. In this case, as long as either one of the two pins 181 and 182 in the bi-pin socket 255 and either one of the two pins 183 and 184 in the bi-pin socket 256 receive power, the LLT lamps can operate.
In the U.S. Pat. No. 8,147,091, issued Apr. 3, 2012, the entirety of which is incorporated herein by reference, double shock protection switches are used in a double-ended LLT lamp to isolate its LED driver such that a leakage current flowing from a live bi-pin, through the LED driver, to an exposed bi-pin is eliminated without shock hazards. FIGS. 5 and 6 illustrate an LLT lamp with such shock protection switches. The LLT lamp 200 comprises a housing 201; two lamp bases 260 and 360, one at each end of the housing 201; two actuation mechanisms 240 and 340 of shock protection switches 210 and 310 in the two lamp bases 260 and 360, respectively; an LED driver 400; and LED arrays 214 on an LED PCB 205. Soldering joints 152 and 153 are used to connect the driver output DC+ and DC− to the LED arrays.
FIG. 6 is a block diagram of an LLT lamp 200 with the shock protection switches 210 and 310. The shock protection switch 210 comprises two electrical contacts 220 and 221 and one actuation mechanism 240. Similarly, a shock protection switch 310 comprises two electrical contacts 320 and 321 and one actuation mechanism 340. The electrical contact 220 in the shock protection switch 210 connects electrically to the bi-pin 250 that connects to the L wire of the AC mains, and the other contact 221 connects to one of the inputs 270 of the LED driver 400. Similarly, the electrical contact 320 in the shock protection switch 310 connects electrically to the bi-pin 350 that connects to the N wire of the AC mains, and the other contact 321 connects to the other input 370 of the LED driver 400. The shock protection switches 210, 310 are normally off. Only after being actuated, will the shock protection switches turn “on” such that they connect the AC mains to the LED driver 400 that in turn powers the LED arrays 214. Serving as gate controllers between the AC mains and the LED driver 400, the shock protection switches 210 and 310 connect the line and the neutral of the AC mains to the two inputs 270 and 370 of the driver 400, respectively. If only one shock protection switch 210 is used at one lamp base 260, and if the bi-pin 250 of this end happens to be first inserted into the live socket at one end of the fixture, then a shock hazard can occur because the shock protection switch 210 already allows the AC power to electrically connect to the driver 400 inside the LLT lamp when the bi-pin 250 is in the socket. Although the LLT lamp 200 is deactivated at the time, the LED driver 400 is live. Without the shock protection switch 310 at the other end of the LLT lamp 200, the driver input 370 connects directly to the bi-pin 350 at the other end of the LLT lamp 200. This presents a shock hazard. However, if the shock protection switch 310 is used in accordance with this application, the current flow to the earth continues to be interrupted until the bi-pin 350 is inserted into the other socket, and the protection switch 310 is actuated. The switch redundancy eliminates the possibility of shock hazard for a person who installs an LLT lamp in the existing fluorescent tube fixture.
Almost all the commercially available LLT lamps today—single-ended, double-ended, or double-ended with double shock-protection switches use wire soldering approach to directly connect the LED driver output to the LED arrays and to directly connect the bi-pins in the end cap to the LED driver inputs. This approach prevents the LED driver used from being easily replaced in the first place. Furthermore, the driver not being mechanically secured may create consumer safety problems whereas the driver being mechanically secured with rivets, screws, or some other improper ways, is even more difficult to be replaced.